The invention relates to locking devices in general, and more particularly to improvements in cylinder locks. Still more particularly, the invention relates to improvements in cylinder locks of the type which can be put to use in motor vehicles, for example, to lock a hood, a door or a glove compartment.
It is already known to provide a cylinder lock with a cylinder having a keyhole and being rotatable in a tubular guide which, in turn, is installed in a case or housing. When the key is withdrawn from the keyhole, the cylinder is automatically locked so that it cannot rotate relative to the guide due to the provision of spring-biased tumblers which release the cylinder for rotation with reference to the guide only in response to proper insertion of a fitting key, i.e., when an authorized person possessing a proper key seeks to open the lock. The cylinder is free to turn relative to the case in response to the application of pronounced torque which suffices to disengage a detent mechanism between the case and the guide. The disengagement of such detent mechanism involves an axial movement of the guide and of the cylinder therein through a distance which suffices to result in expulsion or extraction of a male detent member from a female detent member. The cylinder is normally coupled to a motion transmitting element, e.g., an element which can pivot and/or otherwise move one or more locking bolts between operative and inoperative positions. However, the torque transmitting connection between the motion transmitting element and the cylinder is interrupted when the detent mechanism is inactive. Thus, if an unauthorized person who does not own a fitting key succeeds in rotating the cylinder about its axis, this can take place only by rotating the guide with the cylinder, i.e., subsequent to disengagement of the detent mechanism. Consequently, such rotation of the cylinder with the guide cannot result in opening of the lock because the torque transmitting connection between the cylinder and the motion transmitting element is interrupted when the detent mechanism is deactivated. The tumblers permit the cylinder to turn relative to the guide (and to thus transmit torque to the motion transmitting element) only when the detent mechanism is operative, i.e., the cylinder can turn in the guide and can transmit torque to the motion transmitting element only when the tumblers are moved to inoperative positions by a fitting key which must be properly introduced into the keyhole of the cylinder.
A cylinder lock of the above outlined character is disclosed in published German patent application No. 38 27 418. The cylinder lock of this German application comprises a detent mechanism forming part of an axial clutch which normally couples the cylinder to the motion transmitting element and includes an axially movable clutch portion which is axially movably but non-rotatably carried by the cylinder and is biased axially of the cylinder by a spring of the detent mechanism to normally engage an axially fixed clutch element which can transmit torque to the motion transmitting element. A drawback of such lock is that its space requirements are quite pronounced. This holds especially true for the overall length of the lock, as seen in the axial direction of the cylinder. In fact, the length of the lock between the torque transmitting connection (such connection embodies the detent mechanism) and the motion transmitting element almost matches the length of the assembly including the cylinder and its guide. Moreover, the just described cylinder lock comprises a large number of parts.
European Pat. No. 0 139 550 discloses a cylinder lock which also comprises a tubular guide for a cylinder. The cylinder has a keyhole and is normally non-rotatably locked to the guide by a set of tumblers except when the keyhole receives a fitting key. The guide is installed in the case and is held against rotation relative to the case by a detent mechanism having a socket in the peripheral surface of the guide and a spring-biased ball which is mounted in the case and is receivable in the socket to hold the guide against rotation in the case. The ball must be expelled from the socket, by moving radially of the guide, in order to permit rotation of the guide in the socket. The guide further comprises an axially extending projection which cooperates with a reciprocable coupling member. When the cylinder of this lock is rotated by a properly inserted fitting key, the reciprocable member moves away from the projection of the guide so that the coupling can establish a torque transmitting connection between the cylinder and a motion transmitting element which initiates the actual locking or unlocking operation. If a burglar or another unauthorized person attempts to forcibly turn the cylinder with an implement other than a fitting key, the guide rotates with the cylinder because the detent mechanism is disengaged. Consequently, the projection of the guide remains in the path of movement of the reciprocable pusher and prevents the latter from establishing a torque transmitting connection between the cylinder and the motion transmitting element, i.e., between the cylinder and that part or those parts which must be rotated or otherwise moved in order to open the lock. Thus, the fact that an unauthorized person suceeds in turning the cylinder with an implement other than a fitting key entails rotation of the guide for the cylinder but not the establishment of a proper connection between the cylinder and the motion transmitting element. Moreover, the aforementioned reciprocable pusher of the connection between the cylinder and the motion transmitting element is not affected by a shifting of the ball forming part of the detent mechanism between the guide and the case when the cylinder is rotated by an implement other than a fitting key, e.g., by a burglar's tool.
French Pat. No. 1.046.542 discloses a cylinder lock wherein a split guide for the cylinder includes a first portion with three pairs of pin-shaped tumblers and a second portion with two pairs of pin-shaped tumblers. The first portion of the guide must be rigidly secured to and installed in a door or the like, and the second portion has limited freedom of angular movement relative to the first portion. A detent mechanism is provided to normally prevent rotation of the second portion of the composite guide relative to the first portion, and such detent mechanism acts in the axial direction of the cylinder and its guide. When the detent mechanism is disengaged or deactivated as a result of axial movement of at least one of its parts, the second portion of the guide can turn relative to the first portion; however, a coupling between the cylinder and a motion transmitting element is then disengaged as a result of deactivation of the detent mechanism. A fitting key can be used to rotate the cylinder relative to both portions of the guide, and such rotation entails a corresponding movement of the motion transmitting element because the coupling is engaged. If an unauthorized person uses a burglar's tool or another implement to forcibly rotate the cylinder, the latter can be rotated relative to the first portion of the guide in response to exertion of a rather substantial force. This results in destruction of the pin-shaped tumblers in the first portion of the guide. The torque transmitting connection between the cylinder and the second portion of the guide continues to exist so that further rotation of the cylinder (relative to the first portion of the guide) entails rotation of the second portion relative to the first portion whereby the detent mechanism between the two portions of the guide is deactivated. This, in turn, results in disengagement of the coupling between the cylinder and the motion transmitting element, i.e., the latter cannot be rotated by the rotating cylinder. A drawback of the just discussed patented cylinder lock is that the two-piece guide must be replaced with a fresh (intact) guide after each attempt to open the lock with an implement other than a fitting key. The reason is that the pin-shaped tumblers of the first portion of the guide are destroyed when the cylinder is rotated relative to such portion with a tool other than a fitting key.